Photovoltaic cells convert solar energy into electrical energy. Prior to the invention of the photovoltaic cell, however, solar energy was still used as a heat source to heat various materials. For example, solar energy can be used to heat the working fluid in a water heater or heat engine. Because the goal of solar heating systems is the transfer of thermal energy to a medium, reflectors were designed to concentrate the radiation from the heat source, typically the sun, onto the material being heated. Many of these reflectors were trough-shaped to achieve a sharp linear focus capable of delivering high concentrations of thermal energy.
After the invention of the photovoltaic cell, the same trough-shaped reflectors previously used to concentrate solar energy for heating were employed with the intent of concentrating light onto a photovoltaic cell to increase the performance of the cell. Early adopters of trough collector technology failed to recognize, however, that solar cells that convert visible and near infrared radiation (i.e., having a wavelength less than 1 micron) into electricity perform optimally under irradiation conditions very different from those required for the optimum collection of thermal energy. Specifically, the heat load introduced by focusing an image of the sun on silicon solar cells reduces their efficiency. In addition, most solar cells mass-produced today are larger than the solar image formed by focusing reflectors of practical focal length. As a result, the ability of the photovoltaic cells to convert light to electricity was underutilized because the entire surface of the cells was not exposed to solar energy, and the portions that were exposed received such concentrated heat loads so as to affect the cells' efficiency.
A few attempts have been made at designing a reflector system that utilizes more of the surface area of current solar cells and reduces the efficiency-draining effect of high heat loads. For example, it has been observed that displacing the receiver a fixed distance from the sharp focus of a parabolic reflector distributes the solar radiation, as well as the resulting heat load, over the surface of the cell.
Despite such developments, the positioning of a photovoltaic cell with respect to a solar radiation reflector is only one factor that affects the performance and desirability of a solar energy collection system. Many other considerations must be addressed to produce a cost-effective system for the collection and conversion of solar energy that can be readily mass-produced. For example, one such consideration is the total weight of the system. Practitioners of the art recognize that for a concentrating solar collection system to be effective, the system should be mounted on a device that tracks the sun to maintain a high concentration of solar energy on the photovoltaic receiver. The lighter the concentrating solar collection system, the less support is required to carry the system and the less power is required to orient the system with respect to the sun. Accordingly, it is advantageous to minimize the moving weight of these systems to save on material costs for the support structure and limit power losses associated with energizing the tracking system.
Other factors that should be considered in designing a solar energy collection system include ease of manufacturing, cost of manufacture, and durability. For instance, a collection system that requires injection molding or precise machining in order to construct a reflector system that increases photovoltaic efficiency may not be cost effective to mass produce. In addition, reflector systems that require glass or other fragile materials may be unsuitable for outdoor use due to potential wind or other damage.
In light of the factors that should be considered when creating a concentrating solar collection system, there exists a need for reflector assemblies, systems, and methods for collecting solar radiation for photovoltaic electricity generation.